The previous grant period established the structure-function relationships whereby salivary statherin and mucins take part in different hard tissue lubrication regimes. The renewal application proposes to define further and then enhance the physicochemical properties of lubricants at the enamel interface. The identification of new high lubricity amphipaths may lead to treatment modalities for the clinical manifestations of dental abrasion and attrition. The immediate objectives are the establishment of the complete paradigm of the boundary lubrication of enamel. We propose to study small model amphipathic compounds which will then assist us in the design of more complex macromolecules including statherin mutants developed in Subproject I.B. Different modes of delivery of lubricant molecules to enamel surface will be explored including: 1) model compounds in aqueous solutions; 2) insoluble films deposited on enamel from nonaqueous solvents; and 3) slow release delivery from dental material such as composite resins. These formats cover the spectrum of clinical possibilities and should lead to real systems capable of reducing interdental friction coefficient below 0.1 for prolonged periods of time. Investigations on natural salivas, purified mucins, mucin derivatives, and mucin/albumin complexes will also include water evaporative loss which is controlled by colligative properties and the rheological characteristics. These studies may elucidate the role of mucin solvation in the thick film component of thin film lubrication. Collectively, these studies will set new criteria for the performance of salivary substitutes which will include lubricity, water retention and flow characteristics, and in this way to enhance or improve upon the protective properties of saliva.